netdev - Re: [PATCH] igmp: fix ip_mc_sf

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Message-Id: <20100103.215441.43026709.davem@davemloft.net>
Date:	Sun, 03 Jan 2010 21:54:41 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	fleitner@...hat.com
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH] igmp: fix ip_mc_sf_allow race

From: Flavio Leitner <fleitner@...hat.com>
Date: Wed, 30 Dec 2009 12:23:25 -0200

> Almost all igmp functions accessing inet->mc_list are protected by
> rtnl_lock(), but there is one exception which is ip_mc_sf_allow(),
> so there is a chance of either ip_mc_drop_socket or ip_mc_leave_group
> remove an entry while ip_mc_sf_allow is running causing a crash.
> 
> Signed-off-by: Flavio Leitner <fleitner@...hat.com>

Have you triggered this in practice or is this due purely
to code inspection?

That new synchronize_rcu() is very expensive and will decrease
the rate at which groups can be joined and left, _especially_
on high cpu count machines.

I do not think it is therefore a suitable problem to this
race, if it does in fact exist.
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